User guide

Appendix F - Automatic Switching F-11
Load Switch Example
3. The STDMA Hub Controller compares the remote CDM-570/570L’s pre-
selected buffer limits with its buffer status and if the buffer status exceeds
the preselected limits the STDMA Hub Controller increases the time-slot
allocated to that channel. If this brings the buffer status within established
limits no further changes are made.
4. If the buffer status continues to exceed the preselected limits, the STDMA
Controller sends an Automatic Switch Request (ASR) to the VMS.
5. The VMS processes the switch request by checking for available resources
by:
• Determining if there is a free demodulator.
• Determining the channel space (bandwidth) requirements to accommodate
the data flow requested by the STDMA Hub Controller.
6. If the VMS finds available resources it processes the switch request and
sends tuning commands which switches the remote CDM-570/570L out of
STDMA into SCPC mode.
The ideal condition being looked for is that about 90% utilization of the
channel be achieved striving to optimize the use of available bandwidth.
The CDM-570/570L continuously monitors traffic flow volume Whenever a
preset upper or lower limit is exceeded, the CDM-570/570L sends a request
to VMS to change bandwidth by the amount needed to meet the new
requirement. By this process, the bandwidth is continuously optimized in real
time, precisely accommodating circuit traffic volume.
The ability to actually accomplish this is limited by the currently available
carrier bandwidth, and ultimately the power output and antenna size available
at the transmitting remote site.
If the VMS does not have available bandwidth it will ignore the STDMA
Hub Controller’s request for increased bandwidth. The STDMA Hub
Controller will continue to receive buffer status reports from the remote
CDM-570/570L indicating that buffer flow is continuing. The STDMA Hub
Controller will, in turn, continue to request additional bandwidth from the
VMS. If at any time another service drops making bandwidth available, the
next time the STDMA Hub Controller requests additional bandwidth the
VMS will grant the request.
If the video data stream is completed before the switch in bandwidth is done,
the channel is closed, the bandwidth which had been used is made available
again to the pool, and no further action is taken.